Cam drive gear and valve operating system drive gear for engine

Abstract

A cam drive gear for an engine is described where the distance between the axes of a crankshaft and an idle shaft bearing an idle gear thereon can be made smaller, thereby contributing to a reduction in the size of the engine. In addition, a valve-operating system drive gear for an engine is also described where it is possible to restrain a cam chain from chattering at its portion wrapped around a drive sprocket.

1. A cam drive gear for an engine, comprising an idle gear rotatably borne on an idle shaft supported on an engine main body so as to permit power to be transmitted from a crankshaft, drive sprockets rotatable together with said idle gear, driven sprockets provided on camshafts, and endless form power transmission members wrapped around said drive sprockets and said driven sprockets; a primary drive gear mounted on the crankshaft for transmitting the power of the engine to a transmission, and an idler drive gear having a diameter smaller than a diameter of said primary drive gear and disposed to an outer side of said primary drive gear in the axial direction, said idle gear is meshed with said idler drive gear and said idle shaft has an axis parallel to said crankshaft, and said drive sprockets have at least parts of outer peripheries thereof opposed to said primary drive gear and said drive sprockets are disposed to an inner side of said idle gear in the axial direction and said drive sprockets are coaxial with and adjacent to said idle gear. 
   
   
     2. The cam drive gear for an engine as set forth in  claim 1 , further comprising a primary driven gear meshable with said primary drive gear, said primary driven gear is connected to a clutch disposed at a position opposed to an outer periphery of said idler drive gear and interposed between said crankshaft and said transmission. 
   
   
     3. The cam drive gear for an engine as set forth in  claim 1 , wherein said drive sprockets, said driven sprockets and said power transmission members comprise a pair of banks that are arranged in a V-shape adjacent to a crankcase that rotatably supports said crankshaft thereon, and said banks are mutually adjacently disposed toward one end of said crankshaft in the axial direction, and said drive sprockets of both said banks are formed integral with said idle gear. 
   
   
     4. The cam drive gear for an engine as set forth in  claim 3 , further comprising a guide member making sliding contact with the outer periphery of a first one of said endless form power transmission members, said drive sprockets are arranged coaxially, and wherein an end portion of said guide member adjacent one of said drive sprockets is so formed as to cover at least a portion of the outer periphery of said one drive sprocket around which said first endless form power transmission member is wrapped. 
   
   
     5. The cam drive gear for an engine as set forth in  claim 4 , wherein said end portion of said guide member is so formed as to extend around to a lower side of said one drive sprocket and is astride said endless form power transmission member of the other bank and is supported by a support member fastened to the engine main body. 
   
   
     6. The cam drive gear for an engine as set forth in  claim 5 , wherein said end portion of said guide member and a support portion connected to a guide member of the other of said banks are laid on each other and are supported by said support member and a support boss provided on said engine main body for fastening said support member. 
   
   
     7. The cam drive gear for an engine as set forth in  claim 1 , wherein said idle shaft has an eccentric shaft portion, and said idle shaft is supported on said engine main body so as to permit regulation of the position of said idle shaft about an axis set off from an axis of said eccentric shaft portion, and said idle gear is rotatably borne on said eccentric shaft portion through a needle bearing. 
   
   
     8. The cam drive gear for an engine as set forth in  claim 1 , further comprising a guide member making sliding contact with the outer periphery of a first one of said endless form power transmission members, wherein an end portion of said guide member adjacent one of said drive sprockets is so formed as to cover at least a portion of the outer periphery of said one drive sprocket around which said first endless form power transmission member is wrapped. 
   
   
     9. The cam drive gear for an engine as set forth in  claim 8 , wherein said end portion of said guide member is so formed as to extend around to a lower side of said one drive sprocket and is supported by a support member fastened to the engine main body. 
   
   
     10. A valve-operating system drive gear for an engine, comprising first and second power transmission means each comprising a driven sprocket provided on a camshaft that is rotatably borne on a cylinder head a drive sprocket operated in conjunction with the rotation of a crankshaft an endless form cam chain wrapped around said drive sprocket and said driven sprocket, and a chain guide member making sliding contact with the outer periphery of said cam chain; the first and second power transmission means being disposed respectively in first and second banks arranged in a V shape, said drive sprockets in both said banks being aranged coaxially, wherein
 in said power transmission means on at least one side of said first and second banks, an end portion of said chain guide member adjacent said drive sprocket is so formed as to cover at least a portion of the outer periphery of said drive sprocket around which said cam chain is wrapped; 
 said end portion of said chain guide member being formed as to extend around to a lower side of said drive sprocket of said power transmission means of said one bank and is astride said cam chain of said power transmission means of the other bank and is supported by a support member fastened to an engine main body that includes said cylinder heads; and 
 said end portion of said chain guide member and a support portion connected to said chain guide member of said power transmission means of the other of said banks being laid on each other and being supported by said support member and a support boss provided on said engine main body for fastening said support member. 
 
   
   
     11. A valve-operating system drive gear for an engine as set forth in  claim 10 , wherein said drive sprockets are disposed adjacent a rotary member having an axis parallel to said crankshaft and which is rotated in conjunction with said crankshaft.